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Biomedical subjects

Ming Li

Publications and source records attributed to Ming Li.

At least 91 records · Page 5Linked to original sources
PubMed2006

Real-time interactive MRI-guided cardiac surgery: aortic valve replacement using a direct apical approach.

Minimally invasive cardiac surgery requires arresting and emptying of the heart, which compromises visualization of the surgical field. In this feasibility study a novel surgical procedure is demonstrated in which real-time MRI is used to guide the placement of a prosthetic aortic valve in the beating heart via direct apical access in eight porcine hearts. A clinical stentless bioprosthetic valve affixed to a platinum stent was compressed onto a balloon-tipped catheter. This was fed through a 15-18-mm delivery port inserted into the left ventricular (LV) apex via a minimally invasive subxyphoid incision. Using interactive real-time MRI, the surgeon implanted the prosthetic valve in the correct location at the aortic annulus within 90 s. In four of the animals immediately after implantation, ventricular function, blood flow through the valve, and myocardial perfusion were evaluated with MRI. MRI-guided beating-heart surgery may provide patients with a less morbid and more durable solution to structural heart disease.

Animals↗
PubMed2006

An alternative strategy for high throughput generation and characterization of monoclonal antibodies against human plasma proteins using fractionated native proteins as immunogens.

Construction of a monoclonal antibody (mAb) bank containing a vast variety of antibodies against human tissue proteins is important for proteomic research. A novel strategy of subtractive immunization using fractionated native proteins was developed for high throughput generation of mAb against human plasma proteins. By this novel approach, the bottleneck of antigen preparation can be overcome by combining repeated immunization of animals with subtracted fractions of plasma or tissue proteins and identification of target antigen by immunoprecipitation/mass spectrum strategies. Plasma freshly collected from healthy adults was pooled and three fractions were prepared by size exclusion chromatography. Mice were immunized with the fractionated plasma proteins, and 205 strains of hybridomas secreting mAb were obtained after two-round subtractive immunizations and cell fusions. In the first round, 110 strains of hybridomas were established, in which 77 strains secreting mAb were identified against 10 human plasma high-abundant proteins. In the second round, plasma fraction I was absorbed with mAb against IgM, IgG, ceruloplasmin and haptoglobin. The absorbed fraction I was used as immunogen for the second round immunization and cell fusion. Ninety-five strains of hybridomas secreting mAb were obtained. Although the target antigens of mAb from 82 strains of hybridomas were identified as IgM, IgA, alpha2-macroglobulin and fibrinogen, about 85% antibodies obtained from this round were identified as new antibodies when compared with mAb obtained in the first round immunization with plasma fraction I. The results suggest that subtractive immunization with fractionated plasma proteins followed by identification of antigens with immunoprecipitation/mass spectrum may be an effective approach for rapid preparation of mAb against high-and medium-abundant plasma or tissue proteins.

Amino Acid Sequence↗
PubMed2006

Proteomics-based generation and characterization of monoclonal antibodies against human liver mitochondrial proteins.

Monoclonal antibodies (mAbs) have the potential to be a very powerful tool in proteomics research to determine protein expression, quantification, localization and modification, as well as protein-protein interactions, especially when combined with microarray technology. Thus, a large amount of well-characterized and highly qualified antibodies are needed in proteomics. Purified antigen, which is not always available, has proven to be one of the rate-limiting steps in mAb large-scale generation. Here we describe our strategies to establish a murine hybridoma cell bank for human liver mitochondria using unknown native proteins as the immunogens. The antibody-recognized mitochondrial proteins were identified by MS following immunoprecipitation (IP), and by screening of human liver cDNA expression library. We found that the established antibodies reacted specifically with a number of important enzymes in mitochondria. The subcellular localization of these antigens in mitochondria was further confirmed by immunohistocytochemistry. A panel of antibodies was also tested for their ability to capture and deplete the targeting proteins and complexes from the total mitochondrial proteins. We believe these well-characterized antibodies would be useful in various applications for Human Liver Proteome Project (HLPP) when the scale of this hybridoma cell bank is enlarged significantly in the near future.

Antibodies, Monoclonal↗
PubMed2006

Defining pelvic factors in sphincter-preservation of low rectal cancer with a three-dimensional digital model of pelvis.

PURPOSE: Surgeons often can contribute failure of sphincter-preserving procedure to a limitation of pelvis anatomy; however, they cannot determine definitely which anatomic diameter or spatial factor actually affected the success of the procedure. METHODS: Colorectal surgeons, radiologists, and research fellows collaborated closely to establish a three-dimensional digital model of the pelvis with spiral computerized tomography scanning data of patients with rectal cancer. Retrospective analysis on data of 97 patients with low rectal cancer was performed with this model to identify geometric factors that might affect a successful sphincter preservation procedure for low rectal cancer. RESULTS: A digital pelvic model was established. Multivariate analysis demonstrated that distance from the anal verge, body mass index, and pelvic factors affected the success of sphincter preservation. Sphincter preservation was more likely to succeed when the distance from anal verge was > or =5 cm and body mass index was <25 kg/m(2). Shorter diameter from the upper pubis to the sacrococcyx, distance of sacrococcyx, and excessive curvature of the sacrum predicted failure of sphincter preservation in certain cases. CONCLUSIONS: Pelvic diameters could affect the success of sphincter preservation for low rectal cancer patients besides the distance from anal verge and body mass index.

Anal Canal↗
PubMed2006

A widely applicable protocol for DNA isolation from fecal samples.

Feces are increasingly used as sources of DNA for genetic and ecological research. This paper describes a new method for isolation of DNA from animal feces. This method combines multiple purification steps, including pretreatment with ethanol and TE, an inhibitor-absorber made of starch, the CTAB method, the phenol-chloroform extraction method, and the guanidinium thiocyanate-silica method. The new method is efficient according to PCR results of 585 fecal samples from 23 species and costs much less than the commercial kits. The protocol can be tailored to the specific purpose of examining different diets of animals and can be performed with routine laboratory reagents.

Animals↗
PubMed2006

How antipsychotics work-from receptors to reality.

How does a small molecule blocking a few receptors change a patients' passionately held paranoid belief that the FBI is out to get him? To address this central puzzle of antipsychotic action, we review a framework linking dopamine neurochemistry to psychosis, and then link this framework to the mechanism of action of antipsychotics. Normal dopamine transmission has a role in predicting novel rewards and in marking and responding to motivationally salient stimuli. Abnormal dopamine transmission alters these processes and results in an aberrant sense of novelty and inappropriate assignment of salience leading to the experience of psychosis. Antipsychotics improve psychosis by diminishing this abnormal transmission by blocking the dopamine D2/3 receptor (not D1 or D4), and although several brain regions may be involved, it is suggested that the ventral striatal regions (analog of the nucleus accumbens in animals) may have a particularly critical role. Contrary to popular belief, the antipsychotic effect is not delayed in its onset, but starts within the first few days. There is more improvement in the first 2 weeks, than in any subsequent 2-week period thereafter. However, a simple organic molecule cannot target the complex phenomenology of the individual psychotic experience. Antipsychotics diminish dopamine transmission and thereby dampen the salience of the pre-occupying symptoms. Therefore, in the initial stage of an antipsychotic response, the patients experience a detachment from symptoms, a relegation of the delusions and hallucinations to the back of their minds, rather than a complete erasure of the symptoms. Only with time, and only in some, via the mediation of new learning and plasticity, is there a complete resolution of symptoms. The implications of these findings for clinical care, animal models, future target discovery and drug development are discussed.

Animals↗
PubMed2006

Gene silencing in Xenopus laevis by DNA vector-based RNA interference and transgenesis.

A vector-based RNAi expression system was developed using the Xenopus tropicalis U6 promoter, which transcribes small RNA genes by RNA polymerase III. The system was first validated in a Xenopus laevis cell line, designing a short hairpin DNA specific for the GFP gene. Co-transfection of the vector-based RNAi and the GFP gene into Xenopus XR1 cells significantly decreased the number of GFP-expressing cells and overall GFP fluorescence. Vector-based RNAi was subsequently validated in GFP transgenic Xenopus embryos. Sperm nuclei from GFP transgenic males and RNAi construct-incubated-sperm nuclei were used for fertilization, respectively. GFP mRNA and protein were reduced by approximately 60% by RNAi in these transgenic embryos compared with the control. This transgene-driven RNAi is specific and stable in inhibiting GFP expression in the Xenopus laevis transgenic line. Gene silencing by vector-based RNAi and Xenopus transgenesis may provide an alternative for 'repression of gene function' studies in vertebrate model systems.

Animals↗
PubMed2006

A gene locus responsible for reticulate pigmented anomaly of the flexures maps to chromosome 17p13.3.

Reticulate pigmented anomaly of the flexures (RPAF), also called Dowling-Degos disease, is a rare autosomal-dominant cutaneous disorder characterized by spotted and reticulate pigmentation of the flexures. The gene, or even the chromosomal location, for RPAF has not yet been identified. In this study, one Chinese family with RPAF was identified and subjected to a genomewide screen for linkage analysis. We identified a locus at chromosome 17p13.3 with a maximum two-point limit of detection score of 3.61 at markers D17S831and D17S1866 (at recombination fraction theta=0.00). Haplotype analyses indicated that the disease gene is located within the 6.8 cM region distal to D17S1798. It is the first locus identified for RPAF. This study provides a map location for isolation of a disease gene causing RPAF.

Acanthosis Nigricans↗
PubMed2006

All-trans retinoic acid induces XAF1 expression through an interferon regulatory factor-1 element in colon cancer.

BACKGROUND & AIMS: X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) is a novel tumor suppressor and interferon (IFN)-stimulated gene. All-trans retinoic acid (ATRA) exerts an antiproliferative effect on tumor cells through up-regulation of IFN regulatory factor 1 (IRF-1) and the downstream IFN-stimulated genes. The aim of this study was to determine the effect and mechanism of ATRA on XAF1 expression and the role of XAF1 in ATRA-induced growth inhibition in colon cancer. METHODS: Gene expression is detected by reverse-transcription polymerase chain reaction and immunoblotting. The transcription activity of XAF1 promoter is examined by luciferase reporter assay. The activity of IFN regulatory factor binding element (IRF-E) is assessed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Cell growth is evaluated by both in vitro and in vivo in nude mice xenografts. RESULTS: IFN-alfa stimulates XAF1 promoter activity in the colon cancer cells Lovo and SW1116 dose-dependently. An IRF-1 binding element (IRF-E-XAF1) is found in the -30 to -38 nucleotide region upstream of the ATG initiator codon of the XAF1 gene. Site-directed mutagenesis of IRF-E-XAF1 abrogates native and IFN-induced promoter activity and binding capacity. ATRA induces XAF1 expression both in vitro and in vivo through interaction with IRF-E-XAF1. Overexpression of XAF1 increases cell susceptibility to ATRA-induced growth suppression both in vitro and in vivo. Furthermore, the effect of ATRA on XAF1 expression is independent of the promoter methylation and the subcellular distribution of XIAP. CONCLUSIONS: XAF1 participates in ATRA-induced growth suppression through IRF-1-mediated transcriptional regulation.

Adaptor Proteins, Signal Transducing↗
PubMed2006

The prevalence and spectrum of thalassemia in Shenzhen, Guangdong Province, People's Republic of China.

Thalassemia (thal) is the most common autosomal disorder in southern China. The aim of the present study was to investigate the prevalence and spectrum of thalassemia mutations in the population of Shenzhen, Guangdong Province. In total, 3,711 samples from two hospitals in Shenzhen were subjected to hematological and molecular analysis. Of these, 241 (6.49%) were carriers of thalassemias, of which 161 (4.34%) had alpha-thal, 74 (1.99%) had beta-thal, and six (0.16%) had both alpha- and beta-thal. Three deletional and one nondeletional alpha-thal mutation, and nine beta-thal mutations were identified. Compared with other areas in Guangdong Province, the prevalence of thalassemia in Shenzhen was lower, while there was no evident difference for the spectrum of mutations. These results will provide a reference for prenatal testing and genetic counseling in the area.

China↗
PubMed2006

Dopamine, prediction error and associative learning: a model-based account.

The notion of prediction error has established itself at the heart of formal models of animal learning and current hypotheses of dopamine function. Several interpretations of prediction error have been offered, including the model-free reinforcement learning method known as temporal difference learning (TD), and the important Rescorla-Wagner (RW) learning rule. Here, we present a model-based adaptation of these ideas that provides a good account of empirical data pertaining to dopamine neuron firing patterns and associative learning paradigms such as latent inhibition, Kamin blocking and overshadowing. Our departure from model-free reinforcement learning also offers: 1) a parsimonious distinction between tonic and phasic dopamine functions; 2) a potential generalization of the role of phasic dopamine from valence-dependent "reward" processing to valence-independent "salience" processing; 3) an explanation for the selectivity of certain dopamine manipulations on motivation for distal rewards; and 4) a plausible link between formal notions of prediction error and accounts of disturbances of thought in schizophrenia (in which dopamine dysfunction is strongly implicated). The model distinguishes itself from existing accounts by offering novel predictions pertaining to the firing of dopamine neurons in various untested behavioral scenarios.

Action Potentials↗
PubMed2006

Conversion of taxane glycosides to 10-deacetylbaccatin III.

10-Deacetylbaccatin III (10-DAB III) (2) was obtained by a series of treatment of a mixture of taxane glycosides (3, 4, and 5) without isolation before treatment. Since the taxane glycosides are isolated with paclitaxel from yew trees and can be found during the process of the production of paclitaxel, their conversion to 10-DAB III improves the total yield of paclitaxel (1) and docetaxel.

Chromatography, High Pressure Liquid↗
PubMed2006

Optimizing multiple spaced seeds for homology search.

Optimized spaced seeds improve sensitivity and specificity in local homology search. Several authors have shown that multiple seeds can have better sensitivity and specificity than single seeds. We describe a linear programming (LP)-based algorithm to optimize a set of seeds. Theoretically, our algorithm offers a performance guarantee: the sensitivity of a chosen seed set is at least 70% of what can be achieved, in most reasonable models of homologous sequences. In practice, our algorithm generates a solution which is at least 90% of the optimal. Our method not only achieves performance better than or comparable to that of a greedy algorithm, but also gives this area a mathematical foundation.

Algorithms↗
PubMed2006

Effect of antibody to CD134 on perforin-mediated cytolysis in human peripheral blood mononuclear cells.

CD134 (OX40) is a new member of the tumor necrosis factor receptor (TNFR) superfamily. The influence of CD134 on perforin-mediated cytolysis remains obscure. In this study, human peripheral blood mononuclear cells (PBMC) were induced with phytohemagglutinin (50 microg/mL), by using anti-CD134 blocking monoclonal antibody (MAb; 1, 5, and 10 microg/mL) for 6, 12, 24, and 48 h. Perforin-mediated cytolysis against human erythrocytes of PBMC was detected. The expression of perforin mRNA and protein was also measured by reverse transcription-polymerase chain reaction and flow cytometry. Our data showed that the perforin-mediated cytolysis of PBMC was downregulated by various concentrations of anti-CD134 blocking MAb for different times and reached a minimum at 24 h at any concentration. Anti-CD134 blocking MAb induced downregulation of perforin-mediated cytolysis of PBMC in a dose-dependent manner in the range of 1-5 microg/mL. Perforin- mediated cytolysis of PBMC reached a plateau when the concentration of anti-CD134 blocking MAb exceeded 5 microg/mL. Anti-CD134 blocking MAb also induced the inhibition of the expression of perforin protein and mRNA in PBMC. In conclusion, anti-CD134 blocking MAb inhibits perforin-mediated cytolysis of PBMC by, at least in some part, decreasing the production of preforin, which may be useful in treating several autoimmune diseases.

Antibodies, Blocking↗
PubMed2006

Integrating software into PRA: a software-related failure mode taxonomy.

Probabilistic risk assessment is a methodology to assess the probability of failure or success of a mission. Results provided by the risk assessment methodology are used to make decisions concerning choice of upgrades, scheduling of maintenance, decision to launch, etc. However, current PRA neglects the contribution of software to the risk of failure of the mission. Our research has developed a methodology to account for the impact of software to system failure. This article focuses on an element of the approach: a comprehensive taxonomy of software-related failure modes. Application of the taxonomy is discussed in this article. A validation of the taxonomy and conclusions drawn from this validation effort are described. Future research is also summarized.

Journal Article↗
PubMed2006

Hemin-mediated hemolysis in erythrocytes: effects of ascorbic acid and glutathione.

In the present work, we investigated the effect of ascorbic acid and glutathione on hemolysis induced by hemin in erythrocytes. Ascorbic acid not only enhanced hemolysis, but also induced formation of thiobarbituric acid-reactive substances in the presence of hemin. It has been shown that glutathione inhibits hemin-induced hemolysis by mediating hemin degradation. Erythrocytes depleted of glutathione became very sensitive to oxidative stress induced by hemin and ascorbic acid. H(2)O(2) was involved in hemin-mediated hemolysis in the presence of ascorbic acid. However, a combination of glutathione and ascorbic acid was more effective in inhibiting hemolysis induced by hemin than glutathione alone. Extracellular and intracellular ascorbic acid exhibited a similar effect on hemin-induced hemolysis or inhibition of hemin-induced hemolysis by glutathione. The current study indicates that ascorbic acid might function as an antioxidant or prooxidant in hemin-mediated hemolysis, depending on whether glutathione is available.

Ascorbic Acid↗
PubMed2006

Conformation of the AcrB multidrug efflux pump in mutants of the putative proton relay pathway.

We previously reported the X-ray structures of wild-type Escherichia coli AcrB, a proton motive force-dependent multidrug efflux pump, and its N109A mutant. These structures presumably reflect the resting state of AcrB, which can bind drugs. After ligand binding, a proton may bind to an acidic residue(s) in the transmembrane domain, i.e., Asp407 or Asp408, within the putative network of electrostatically interacting residues, which also include Lys940 and Thr978, and this may initiate a series of conformational changes that result in drug expulsion. Herein we report the X-ray structures of four AcrB mutants, the D407A, D408A, K940A, and T978A mutants, in which the structure of this tight electrostatic network is expected to become disrupted. These mutant proteins revealed remarkably similar conformations, which show striking differences from the previously known conformations of the wild-type protein. For example, the loop containing Phe386 and Phe388, which play a major role in the initial binding of substrates in the central cavity, becomes prominently extended into the center of the cavity, such that binding of large substrate molecules may become difficult. We believe that this new conformation may mimic, at least partially, one of the transient conformations of the transporter during the transport cycle.

Amino Acid Substitution↗